Desiccants are commonly employed to maintain the moisture content of a closed system at a low level. Desiccant materials such as silica gel and molecular sieve, for example, have a large surface area for adsorbing moisture. However, conventional desiccant packagings may not be suitable for high reliability applications that require a clean environment. For example, one problem with conventional desiccant materials is that they can release fine particles, which can contaminate the clean environment.
Another problem arises when the closed system is to be operational for an extended period of time (e.g., one or more decades) without being available for maintenance. In such situations the capacity of the desiccant should not be exhausted during the operational life of the system since there is no opportunity to replace the desiccant material. The rate at which the desiccant capacity is exhausted is of particular concern when the closed system must undergo an assembly process that can last for hours or even days. While the system is exposed to the larger environment during assembly, and hence more moisture will be able to reach the desiccant in a shorter period of time, prematurely exhausting the desiccant capacity even before the system is closed. Common desiccant materials absorb water rapidly in an open environment, approximately 50% of their capacity in one or two hours.
An example of a closed system of the previously mentioned type is a splice box, which is employed in undersea optical communication systems. One type of splice box serves as a housing for securing cable connectors such as cable-to-cable connectors and cable-to-repeater connectors. Since undersea cables require electrical continuity across their spans and thus across connectors, the splice box must be appropriately insulated. For this reason the splice box undergoes an overmolding process to encase it in polyethylene during its final assembly. The splice box is designed to function undersea for twenty-five or more years without requiring service.
Some splice boxes house additional components such as a gain equalization filter (GEF), for example. This filter is used to adjust the gain among the various optical channels after they undergo amplification in the repeater. To avoid corrosion of the filter, the moisture content of the splice box needs to be maintained at or below a relative humidity of 50%. Since the splice box does not provide a hermetic seal that prevents moisture from entering, the GEF splice box requires a desiccant.
Accordingly, there is need for a desiccant that does not release fine particles or dust and which has a substantially reduced moisture adsorption rate.